This section provides background information related to the present disclosure which is not necessarily prior art.
Present regulatory conditions in the automotive market have led to an increasing demand to improve fuel economy and reduce emissions in present vehicles. These regulatory conditions must be balanced with the demands of a consumer for high-performance and quick response for a vehicle. Cylinder deactivation is a technology that often is applied to naturally aspirated internal combustion engines to improve the engine's efficiencies under part-load conditions by switching off a selected number of cylinders so the remaining cylinders would operate with reduced pumping losses [see “Active Fuel Management Technology: Hardware Development on a 2007 GM 3.9L V-6 OHV SI Engine,” SAE Paper 2007-01-1292, 2007.]
Cylinder deactivation can be applied to turbocharged engines as disclosed in U.S. Pat. Nos. 6,715,289 and 6,786,190. However, when an engine is equipped with a single turbocharger, the operating ranges of the engine in the deactivated mode can be limited by the turbocharger compressor's flow and boost pressure capabilities [see “The 1.4-L TSI Gasoline Engine with Cylinder Deactivation,” MTZ, volume 73, March 2012.]
It is possible to size a turbocharger compressor to favor the deactivated operation of the engine, primarily at lower engine speeds. This would require the use of a smaller compressor, by compromising the engine's performance at high engine speeds. The compressor can be at a size such that a single fixed geometry turbine is not capable of driving the compressor to meet performance requirements. As anticipated, a smaller turbine is desired to meet the low engine speed target while a larger turbine is desired to meet the high engine speed target.
When packaging and complexity are not of concerns, a two-stage turbocharger system can be adopted with greater flexibilities than what can be achieved with a single turbocharger. With the addition of another turbocharger, the so-called high-pressure turbocharger can be sized for the deactivated operation.
The present disclosure provides an enhanced two-stage turbocharger system that is architected for engines featuring cylinder deactivation and its operating modes.